Eggstra, eggstra............. what exactly happens when you bake a cake?

Science (ology) is what happens.  How can three or four pretty bland ingredients be 'voilad' into a wonderful moist, scrumptious cake? What occurs in that mixing bowl and hot place? Some of you will know that you start off by creaming together butter and sugar (in pretty exact quantities!). During this process the butter coats each granule of sugar and air is added, lightening the mix.

The beaten eggs are added, the proteins in which coat the air bubbles and stop them disappearing when heated.

Once you add the self raising flour, which has a chemical leavening agent (baking powder: a dried acid (eg cream of tartar and sodium aluminium sulphate) and an alkali (sodium bicarbonate, or baking soda). Adding water and heat to this mixture allows the acid to react with the alkali to produce carbon dioxide gas. This is trapped in the tiny air pockets created when you creamed the fat and sugar together in the first stage.

Some of the proteins in the flour join together to create an extensive network of coiled proteins, known as gluten. It is this gluten that holds the cake together. Its elastic nature allows the batter to expand during baking (to incorporate gases) and then it coagulates into a strong network that supports the heavy weight of sugar and shortening.

Folding the flour in gently (as Mother always told you) avoids breaking down the bubbles you have worked so hard to put into the mix in the first place. It also reduces excessive gluten formation: Gluten is essential to the structure of the cake, but excessive beating creates too much gluten, resulting in a cake with a heavy texture. Cake flour is made from soft wheats with a low protein content.

So, what happens in the oven?

As the batter temperature rises, the gases in the air cells expand the stretchy gluten from the flour, then the chemical leavening agents release carbon dioxide. (Starting to sound dangerous?). As the batter reaches 60degrees centigrade, water vapour begins to form and expand the air cells. Carbon dioxide and water vapour account for approximately 90% of the subsequent expansion of the batter, the remaining 10% being due to thermal expansion. At around 80 degrees, the risen batter adopts its permanent shape as the egg proteins set, starch granules absorb water, swell and form a gel, and the gluten loses its elasticity.

Finally, flavour-enhancing browning (Maillard) reactions take place on the surface. It is at this point you have to decide whether the cake is ready – one of the most critical points in the whole process. The cake will shrink slightly away from the walls of the tin and the crust will spring back when touched with a finger.(A knife or skewer inserted in the centre of the cake should come out clean).

Bakers? nooooo, we're scientists, it's official!